Map of current U.S. states that are direct successor states of the original Thirteen Colonies that declared independence from Great Britain in 1776. Indirect successor states (Maine, Kentucky, West Virginia), the District of Columbia and states that acceded to the union after the American Revolutionary War are not included

National Atlas map (circa 2005) depicting territorial acquisitions.

A government map, probably created in the mid-20th century, that depicts a simplified history of territorial acquisitions within the continental United States

The Louisiana Purchase in 1803, was negotiated with Napoleon during the presidency of Thomas Jefferson; the territory was acquired from France for $15 million (equivalent to $245 million in present-day terms). A small portion of this land was ceded to Britain in 1818 in exchange for the Red River Basin. More of this land was ceded to Spain in 1819 with the Florida Purchase, but was later reacquired through Texas annexation and Mexican Cession.[2]

West Florida was declared to be a U.S. possession in 1810 by President James Madison after the territory had declared its independence from Spain.[3] Madison ordered the U.S. Army to take control. Six weeks later, the army entered and occupied the capital, St. Francisville, putting an end to the republic after 74 days of independence. Spain did not relinquish its claim to sovereignty (see West Florida Controversy) until ratification of the Adams–Onís Treaty. General Andrew Jackson personally accepted the delivery of West Florida from its Spanish governor on July 17, 1821.[4]

In the Gadsden Purchase of 1853, the United States purchased a strip of land along the Mexico–United States border for $10 million (equivalent to $294 million in present-day terms), now in New Mexico and Arizona. The territory was also bought as Americans were passing through the land west to California. After the American Mexican War, over the dispute of border claims, American bought the land to prevent future conflict. Few historians would argue the territory was intended for a southern transcontinental railroad.

Alaska Purchase from the Russian Empire for $7.2 million (2 cents per acre)[8] on March 30, 1867 (equivalent to $126 million in present-day terms), as a vital refueling station for ships trading with Asia. The land went through several administrative changes before becoming an organized territory on May 11, 1912, and the 49th state of the U.S. on January 3, 1959.

With Hawaii came two remote coral atolls: the Palmyra Atoll which had been annexed by the U.S. in 1859, abandoned, then claimed in 1862 by the Kingdom of Hawaii, and the Stewart Islands, which had joined the Kingdom a few years before Palmyra. At Hawaiian statehood in 1959, Palmyra and arguably the Stewarts were excluded from the new state. Palmyra remained an incorporated U.S. territory, while the Stewarts were claimed and are now controlled by the Solomon Islands.[9]

Puerto Rico, Guam, and the Philippines (for which the United States compensated Spain $20 million, equivalent to $588 million in present-day terms), were ceded by Spain after the Spanish–American War in the 1898 Treaty of Paris. Spain relinquished all claim of sovereignty over Cuba, but did not cede it to the United States, so it became a protectorate. All four of these areas were under United States Military Government (USMG) for extended periods. Cuba became an independent nation in 1902, and the Philippines became an independent nation in 1946.

During this same period the American people continued to strongly chastise the European powers for their imperialism. The Second Boer War was especially unpopular in the United States and soured Anglo-American relations. The anti-imperialist press would often draw parallels between the U.S. in the Philippines and the British in the Second Boer War.[10]

Under the 1898 Treaty of Paris, Spain relinquished all claim of sovereignty over and title to Cuba, with the island to be occupied by the United States. Under the Teller Amendment Congress had already decided against annexation. Cuba gained formal independence on 20 May 1902. Under the new Cuban constitution, however, the U.S. retained the right to intervene in Cuban affairs and to supervise its finances and foreign relations through the Platt Amendment;[11] this, however, was later renounced as part of Franklin Roosevelt's Good Neighbor Policy.[11] Under the Platt Amendment (1901), Cuba also agreed to lease to the U.S. the naval base at Guantánamo Bay.

The naval base occupies land which the United States leased from Cuba in 1903 "... for the time required for the purposes of coaling and naval stations." The two governments later agreed that, "So long as the United States of America shall not abandon the said naval station of Guantanamo or the two Governments shall not agree to a modification of its present limits, the station shall continue to have the territorial area that it now has, with the limits that it has on the date of the signature of the present Treaty."[12][13]

On July 25, 1898, during the Spanish–American War, Puerto Rico was invaded by the United States with a landing at Guánica. As an outcome of the war, the Jones–Shafroth Act granted all the inhabitants of Puerto Rico U.S. citizenship in 1917. The U.S. granted Puerto Ricans the right to democratically elect their own governor in 1948. In 1950, the Truman Administration allowed for a democratic referendum in Puerto Rico to determine whether Puerto Ricans desired to draft their own local constitution without affecting the unincorporated territory status with the U.S.[14] A local constitution was approved by a Constitutional Convention on February 6, 1952, ratified by the U.S. Congress, approved by President Truman on July 3 of that year, and proclaimed by Gov. Muñoz Marín on July 25, 1952, the anniversary of the 1898 arrival of U.S. troops. Puerto Rico adopted the name of Estado Libre Asociado (literally translated as "Free Associated State"), officially translated into English as Commonwealth, for its body politic.[15][16]

In Guam, settlement by foreign ethnic groups was small at first. After World War II showed the strategic value of the island, construction of a huge military base began along with a large influx of people from other parts of the world. Guam today has a very mixed population of 164,000. The indigenous Chamorros make up 37% of the population. The rest of the population consists mostly of white Americans and Filipinos, with smaller groups of Chinese, Japanese, Koreans, Micronesians, Vietnamese and Indians. Guam today is almost totally Americanized. The situation is somewhat similar to that in Hawaii, but attempts to change Guam's status as an 'unincorporated' U.S. territory have yet to meet with success.

The Philippine Organic Act of 1902 provided for the establishment of a bicameral legislature composed of an upper house consisting of the Philippine Commission, an appointed body with both American and Filipino members. and a popularly elected lower house, the Philippine Assembly. The Philippines became a U.S. colony in the fashion of Europe's New Imperialism,[citation needed] with benevolent colonial practices. English joined Spanish as an official language, and English language education was made compulsory. In 1916, the United States passed the Philippine Autonomy Act and committed itself to granting independence to the Philippines "as soon as a stable government can be established therein."[19] As a step to full independence in 1946, partial autonomy as a Commonwealth was granted in 1935.

Germany, the United States, and Britain colonized the Samoan Islands. The nations came into conflict in the Second Samoan Civil War and the nations resolved their issues, establishing American Samoa as per the Treaty of Berlin, 1899. The U.S. took control of its allotted region on June 7, 1900, with the Deed of Cession. Tutuila Island and Aunuu Island were ceded by their chiefs in 1900, then added to American Samoa. Manua was annexed in 1904, then added to American Samoa. Swains Island was annexed in 1925 (occupied since 1856), then added to American Samoa. (The claim is currently disputed by Tokelau, a colonial territory of New Zealand.) American Samoa was under the control of the U.S. Navy from 1900 to 1951. American Samoa was made a formal territory in 1929. From 1951 until 1977, Territorial Governors were appointed by the Secretary of the Interior. Immigration of Americans was never as strong as it was, for instance, in Hawaii; indigenous Samoans make up 89% of the population. The islands have been reluctant to separate from the U.S. in any manner.

The Annexation of Santo Domingo was an attempted treaty during the later Reconstruction Era, initiated by United States President Ulysses S. Grant in 1869, to annex "Santo Domingo" (as the Dominican Republic was then commonly known) as a United States territory, with the promise of eventual statehood. President Grant feared some European power would take the island in violation of the Monroe Doctrine. He privately thought annexation would be a safety valve for African Americans who were suffering persecution in the US, but he did not include this in his official messages. Grant speculated that the acquisition of Santo Domingo would help bring about the end of slavery in Cuba and elsewhere. Militarily he wanted a US naval port in the Dominican Republic which would also serve as protection for a projected canal across Nicaragua.

On January 10, 1870 President Grant formally submitted Sec. Fish's Dominican Republic annexation treaty to the U.S. Senate. The treaty was stalled in the Senate until Sen. Sumner's Foreign Relations Committee started hearings in mid February, 1870. On 19 February, a referendum was held in the Dominican Republic, in which nearly 99% of the votes cast were in favor of the annexation. Sec. Fish noted that the Senate was reluctant to pass any measures initiated by the Executive Branch. Sen. Sumner allowed the treaty to be debated openly on the Committee without giving his own opinion. However, on March 15, Senator Sumner's Foreign Relations Committee in a closed session voted to oppose the treaty 5 to 2. On March 24, in another closed session, Sen. Sumner came out strongly against the treaty. Sen. Sumner opposed the treaty believing annexation would be expensive, launch an American empire in the Caribbean, and would diminish independent Afro-Hispanic and African creole republics in the Western Hemisphere. Grant met with many Senators on Capitol Hill hoping to rally support for the Treaty, however, to no avail. Grant refused the suggestion that the treaty drop the Dominican statehood clause. Finally on June 30, 1870 the Senate defeated the Dominican Republic Annexation treaty by a vote of 28 to 28. Eighteen Senators had joined Sen. Sumner to defeat the Dominican annexation treaty.

The first United States occupation of the Dominican Republic lasted from 1916 to 1924. It was one of the many interventions in Latin America undertaken by the military forces of the United States. On May 13, 1916, Rear Admiral William B. Caperton forced the Dominican Republic's Secretary of War Desiderio Arias, who had seized power from Juan Isidro Jimenes Pereyra, to leave Santo Domingo by threatening the city with naval bombardment.

From the start of the intervention until the US Marines withdrew in 1924, they were in almost continuous actions on both the squad and platoon levels, fighting numerous small-unit actions with elusive guerilla forces. Despite the ability of the Marines to bring a large amount of firepower to bear against the guerillas from both the ground and the air, the occupation troops had their share of problems as well. Sometimes the enemy would successfully ambush a lone Marine patrol, killing all or most of its members, and would scatter before reinforcements arrived on the scene.

In 1917, the United States purchased the former Danishcolony of St. Croix, St. John and St. Thomas, which is now the U.S. Virgin Islands. The United States—which had made an earlier approach in 1902—purchased these islands because they feared that the islands might be seized as a submarine base during World War I. After several months of secret negotiations, a sales price of $25 million was agreed. A non-binding referendum in Denmark held in late 1916 confirmed the decision to sell by a wide margin. The U.S. took possession of the islands on March 31, 1917 a few days before the U.S entered the war. The deal was ratified and finalized on January 17, 1917, when the United States and Denmark exchanged their respective treaty ratifications. The territory was renamed the U.S. Virgin Islands.[20] U.S. citizenship was granted to the inhabitants of the islands in 1927.

On November 24, 2009, the U.S. ceded 6 islands in the Rio Grande to Mexico, totaling 107.81 acres (0.4363 km2). At the same time, Mexico ceded 3 islands and 2 cuts to the U.S., totaling 63.53 acres (0.2571 km2). This transfer, which had been pending for 20 years, was the first application of Article III of the 1970 Boundary Treaty.

The Chamizal Treaty of 1963, which ended a hundred-year dispute between the two countries near El Paso, Texas, transferred 630 acres (2.5 km2) from the U.S. to Mexico in 1967. In return, Mexico transferred 264 acres (1.07 km2) to the U.S.

The Rio Grande Rectification Treaty of 1933 straightened and stabilized the 155 miles (249 km) of river boundary through the highly developed El Paso-Juárez Valley. Numerous parcels of land (174) were transferred between the two countries during the construction period, 1935–1938. At the end, each nation had ceded an equal area of land (2,560.5 acres (10.362 km2)) to the other.[21][22]

The Banco Convention of 1905 resulted in many exchanges of bancos (land surrounded by bends in the river that became segregated from either country by a cutoff, often due to rapid accretion or avulsion of the alluvial channel) between the two nations, most often in the Lower Rio Grande Valley. Under the treaty, the following transfers involving Texas occurred from 1910–1976:[23]

Proposed: Based on aerial surveys in 2008, there are 138 cases where the widest channel of normal flow of the Rio Grande has shifted from previous surveys. Therefore, the International Boundary Line is to be changed under Article III of the 1970 Boundary Treaty. The result is 138 proposed transfers of territory that remain pending further evaluation and approval by the International Boundary and Water Commission and the two governments. Upon resolution, the U.S. is to cede 7 islands and 60 cuts in the Rio Grande to Mexico, totaling 1,251.2 acres (5.063 km2), while Mexico is to cede 3 islands and 68 cuts to the U.S., totaling 1,275.9 acres (5.163 km2).

The Northern Mariana Islands were part of the former Trust Territory of the Pacific Islands but decided in the 1970s not to seek independence. The Commonwealth of the Northern Mariana Islands in political union with the United States was established in 1978.

^Miller 1984, p. 163 "... Will Show No Mercy Real Warfare Ahead For Filipino Rebels Kitchener Plan Adopted The Administration Weary of Protracted Hostilities.' The reference to Kitchener made eminently clear MacArthur's intent, as the British general's tactics in South Africa had already earned ..."